Resorcyclic lactone of fungal origin that acts as a potent and selective transforming growth factor-β-activated kinase 1 (TAK1) mitogen-activated protein kinase kinase kinase (MAPKKK) inhibitor (IC50 = 8 nM). Displays > 33-fold and > 62-fold selectivity over MEKK1 and MEKK4 respectively. Inhibits IL-1-induced activation of NF-κB (IC50 = 83 nM) and JNK/p38. Inhibits production of inflammatory mediators, and sensitizes cells to TRAIL- and TNF-α-induced apoptosis in vitro.